Thermoplastic molding produces sprues and other pieces of scrap thermoplastic material in the course of molding articles. Rather than discard this scrap material, it is conventional to the art to grind such scrap into comparatively uniform sized particulate amountable to intermixing with virgin thermoplastic pellets for reprocessing through the molding process. Unfortunately, it is common that debris becomes intermixed with the pelletized thermoplastic scrap. Such debris can compromise the quality of a molded article through creation of an inhomogeneity. This problem is especially severe when molding transparent articles in which debris can form a visually discernible inclusion. Further, depending on the processing conditions and the nature of the debris, charring of the debris can occur resulting in a visually discernable black inclusion.
Furthermore, unwanted foreign spurious metal shavings or particulate may be introduced to molding materials due to mechanical wear of processing machinery. The introduction of metal shavings may also have adverse effects on the molding material properties, performance, and surface finish.
In response to the problems associated with debris becoming entrained with a regrind particle stream or indeed a virgin thermoplastic particle stream, the separators are conventionally used to remove such debris. Conventional separators have included vibratory separators in which material is loaded on to a size exclusion mesh and either manually or mechanically oscillated to shake the debris through the mesh thereby leaving comparatively debris free particulate. However, such vibratory separation schemes require a considerable amount of space and are kinetically slow in separating debris from particulate as a result of electrostatic attraction between the debris and particulate resulting in interparticle transfer of debris as the debris traverses through the particulate before being sieved from the particulate. In response to the limitations of vibratory separation techniques, pressurized air flows have been utilized to flow over a monolayer or several monolayers of particulate to drive the comparatively lighter mass debris from the particles. A number of such systems have also utilized a conveyor or other movement of the material to facilitate such separation. However, pressurized air separation techniques tend to be complex and difficult to maintain on to the inclusion of an air compressor and particle conveyance equipment that increase the footprint of such a separator as well as cost of usage.
Thus, there exists a need for a particle separator that achieves high throughput separation of particulate from debris and foreign metallic mater, and does so with limited complexity and moving components. There further exists a need for a particle separator having a small footprint and operative without a pressurized countercurrent gas flow across the material to be separated